Terrible gas mileage.

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Terrible gas mileage.

tcazes
ok fellas im only getting around 20mpgs on my 82 cb750sc. i put 4 into 1's on the bike because the stock pipes were completely rusted off and clogged. the carbs have 80's? in the mains (i cant really remember) and stock was 68 according to the manual so if anything after the k&n filter, 4 into 1 pipes and all of my needles at around 1 1/4 you wouldnt think it would still be rich and wasting gas so what gives? i do plug chops regularly and she always runs a tad lean (light grey/brown) should i switch to 110 mains? she runs fine really only time its weird is if i try to run steady lower rpms (35-4k) at like 35 or 40mph she will surge a bit. i smelled the oil when i changed it and no gas smell so i believe the petcock is still fine (did manual test into a bottle and it worked properly as well) im at a loss here. stumped.
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Re: Terrible gas mileage.

TOOLS1
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There are a lot of things that can cause poor gas mileage. Have you checked tire pressure/condition of tires? Could a brake be dragging? Wheel bearings going bad?
TOOLS
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1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: Terrible gas mileage.

tcazes
Tires new, pressure good, bearings nice and lubed. front wheel spins freely, rear as well. no dragging anywhere... thanks for the fast response btw! the other site i was on took a week for them to just say get a manual.
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Re: Terrible gas mileage.

MarkPBG
How about the final drive ratio? Changed the chain and sprockets to a different combination?
Mark Davis
Palm Beach Gardens, FL
amateur photographer, hot rodder, motorcyclist, adventurer
"Four wheels move the body. Two wheels move the soul."
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Re: Terrible gas mileage.

tcazes
hmmm i doubt it. the po was pretty lazy. it doesnt seem like it as far as i can tell. it pulls 5k rpms at 65mph. sound about right?
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Re: Terrible gas mileage.

MarkPBG
I don't know, my chain and sprockets have been changed. I run 4K RPM at 65 MPH.
Mark Davis
Palm Beach Gardens, FL
amateur photographer, hot rodder, motorcyclist, adventurer
"Four wheels move the body. Two wheels move the soul."
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Re: Terrible gas mileage.

shinyribs
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In reply to this post by tcazes
5k rpm's @ 65 mph is actually a lower engine speed than the stock gearing (sprocket ratio) will give you.

How do your spark plugs look?
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Re: Terrible gas mileage.

tcazes
Spark plugs always say it's running rich. I can't get them ight to save my life. Most of the time it's dry black soot covering the plug. Guess I should drop the main jets down from the 80s that are in there?
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Re: Terrible gas mileage.

tcazes